is invariably caused by impingement. That's pretty well established. You've been given some sage advice, particularly from ponyboy, "Sciatica is often a problem with the piriformis being too tight.", then he went off the deep end with the incorrect definition of bulging and herniated, which are, as Robert DiMaggio correctly pointed out, synonyms. Ponyboy was right on about the piriformis causing sciatic nerve problems. Anytime you do sit ups with your feet being held down, as soon as your body can (at about 15 deg off the floor) it will engage the strongest muscle for the job, the piriformis. The piriformis is the strongest muscle in your body for it's size. When it hypertrophies (grows from being worked), the belly of the muscle may press the sciatic nerve and tada, you've got misery!
While I generally find Pfunk's advice quite good he's wrong about chiropractic. Like any professionals there are good and bad. I have the best chiropractor in the area as part of my medical support for my athletes. He works wonders. A good chiro may be able to provide some relief through adjustment. The trick is finding a good one. Anything that will increase the space where the nerve is being impinged is going to provide some relief from your pain. The key is the location of impingement.
If it is the disc, simple kick overs may be of help. Lying on you back, with hands behind head and upper body relaxed, bring your legs up to where your calves are parallel to the floor, toes pointed at ceiling, knees bent 90 deg, your thighs are pointing straight up, back completely flat on floor. Now GENTLY bring your feet back, arching your back, belly button curling toward sternum, knees toward chest 'till your feet are over or past (if possible) your head. If the movement causes pain, STOP! (You will anyway, because it'll be a very SHARP! pain).
Return slowly to start position, as though there's a wall to stop your feet, thighs perpendicular to floor, toes pointed at ceiling calves parallel to floor, back flat. Do NOT let your legs go too far! Legs kept in strict L shape, if you go too far the lower back arches, which is not helpful.
If you can do this without irritating the nerve (trust me, you'll know if you are), keep doing them, 20 reps if possible. By activating the abs you'll allow your back muscles to relax a little, and with continued effort, you may be able to open the space between the vertebrae and relieve some of the pressure on the disc and the irritated sciatic nerve.
There is research validating the efficacy of the exercise, it will increase the space between vertabrae. The question is, when? Depends on several factors, so be patient and keep doin' your kick overs.
Lying in the same position, with something to support the lower legs, knees 90deg back completely flat, on a bed of ice for 3 20 min sessions with 20 min in between will reduce swelling and inflamation. Combined with a couple of sprays of Stopain, a topical analgesic (in my opinion, the best) and hopefully, you should be reasonably comfortable and able to sleep.
On a personal note, I have a bilaterally fractured 5th lumbar vertbrae and the fusion surgery did not work so it's still hypermobile. Strong abs, kickovers and a great chiro have allowed me to avoid surgery for 20 years. And I still periodically annoy my athletes by outlifting them.
I hope this helps, please keep us abreast of your progress,
Ubercoach